OBJECTIVE This study describes the prevalence, adequacy and correlates of 12-month mental health service use among participants in the Mexican Adolescent Mental Health Survey. METHODS The authors conducted face-to-face household surveys of a probability sample of 3005 adolescents aged 12-17 years residing in the Mexico City metropolitan area during 2005. The prevalence of mental health disorders and the use of services were assessed with the computer-assisted adolescent version of the World Mental Health Composite International Diagnostic Interview. Correlates of service use and adequate treatment were identified in logistic regression analyses that took into account the complex sample design and weighting process. FINDINGS Less than one in seven respondents with psychiatric disorders used any mental health services during the previous year. Respondents with substance-use disorders reported the highest prevalence of service use and those with anxiety disorders the lowest. Approximately one in every two respondents receiving any services obtained treatment that could be considered minimally adequate. CONCLUSION We found large unmet needs for mental health services among adolescents with psychiatric disorders in Mexico City. Improvements in the mental health care of Mexican youth are urgently needed.